The purpose of this experiment was to determine to what extent individuals could cancel the rotational vestibulo-ocular reflex (RVOR) in order to track an accelerating, high speed ball. More specifically, this study was designed to determine if subjects could successfully track a baseball pitch while viewing the ball through small apertures. While wearing these aperture goggles, we hypothesized that the batsmen would have to increase the rotational amplitude of their heads while successfully suppressing their rotational vestibulo-ocular reflex in order to accurately track a pitched baseball.
Subjects were tested using a pitching machine called the Flamethrower under normal viewing conditions (no apertures), then while wearing apertures that subtended 3.3 degrees of visual field, and finally under normal viewing conditions again. In the final trial (normal viewing), subjects were encouraged to replicate the eye and head movements adopted while wearing the apertures. Tennis balls were pitched from a distance of 44 feet from the batter at a measured velocity of approximately 80 miles per hour. Eye movements were recorded with the ISCAN infrared eye tracker and horizontal head rotations were recorded with the 3DM-GX1 head tracker. All head and eye recordings were temporally synchronized with each other and with ball position using software.
A total of twelve subjects were enrolled in the study. Each subject viewed 50 pitches under each of the above defined testing conditions. A total of 1796 pitches were successfully recorded with nine subjects identified as able to accurately track a tennis ball under all testing conditions. Thus, 1346 pitches were analyzed.
Mean gaze errors for all three trials indicated that the subjects were able to accurately track the pitched tennis balls for a majority of the ball’s flight path under each testing condition. Absolute gaze errors were smallest with the apertures compared to the other conditions at 300, 305, and 339ms after the pitch was released. These results were all statistically significant.
The results of the study revealed consistent statistically significant differences in head movement when wearing the apertures at 200, 250, 300, 305, and 339ms. Specifically, this analysis revealed that the introduction of the apertures resulted in a decrease in head rotation.
Finally, examination of the individual data suggested that in most cases once the aperture was removed, individuals generally did not completely adopt the same eye movements and head movements that had been used with the apertures.
Overall these results suggest that wearing the aperture goggles aided in proper tracking. The improvement in gaze tracking with the apertures indicates that subjects could successfully cancel the RVOR. Further, the apertures generally resulted in a decline in head movement amplitude, in agreement with a previous study showing that individuals tend to show head movement overshoots when aiming the head at moving targets unless provided with a visual cue to head position. Further studies need to be performed to investigate any potential of the apertures to produce behavioral changes post training, and to determine whether these changes in eye and head coordination correlate with batting performance.